Most generic headsets work fine. There's a headset jack on the phone, and invoking the HEADSET feature code causes the regular SPKR button to go on-hook/off hook without any kind of handset lifter...just press the button to answer or hang up, or lift handset to use that.
The above directions don't apply, of course, if you're using one of the wireless headsets that REQUIRE a mechanical lifter...in that case don't change anything, and plug the headset transmitter into the handset jack, then handset into transmitter, and stick lifter in place.